The invention relates to a method of adjusting, in the course of applying predetermined voltages, an oblong piezo-electric bending element which at a first end has been supported by a part protruding in the longitudinal direction of said element, as well as to a piezo-electric bending element as has been constructed by applying the method and also to tools for the application of the method.
A piezo-electric element and its adjustment has been described in the European patent specification 0237090, where a piezo-electric element has been adjusted by securing a fixed end, for instance by means of soldering, after its movable end has been brought in a specific place.
In many cases this method has proved to be sufficiently accurate and is considerably labour-saving, compared to an other possibility of adjustment as has been described in the U.S. Pat. No. 4,473,356, which amounts to this that a sensing pin is set lengthwise between the flexible member and the sensing surface of the braille cell.
The invention aims at providing a method which, after the flexible element has been secured, allows its adjustment, at which instance the method in accordance with the European patent specification 0237090 may or may not have been applied first. In broad outline it can be said that, as a result of the method known from the European patent specification, a good adjustment can be obtained, but that, for a very accurate adjustment and/or the correction of an adjustment that, for example, had been affected due to use, there is a need for a more finely operating process which can be applied to an element after it has completely been installed.
In applying such flexible bending elements for braille cells, it has been observed that the blind are very sensitive to small deviations in the position of the pins, particularly the so-called withdrawn position, and that even the smallest deviations have been found to be very annoying. This invention offers the possibility to adjust such braille cells, not only new cells prior to their delivery but also used ones, the adjustment of which has been worn out.
In order to put the above mentioned possibilities into practice, it is provided in accordance with the invention that the part is mechanically bent and consists of a material in which at least part of the bending deformation is permanent.
It may be observed that the movement of the piezo-electric element is generated due to the fact that this element bends under the influence of applied voltages. This bending relates to the entire element, with three conducting layers and, in between, two layers of piezo-electric material. See Patent Abstracts of Japan 30M 427, 60-122175 (A), or U.S. Pat. No. 4,283,178. In the invention, however, a permanent bending deformation is conveyed to a protruding part.
When applying the invention, the mechanical bending preferably occurs while observing, in relation to a reference point, that portion of the element that, in bending, moves while voltage is being applied.
The protruding part, which is bent when applying the invention, is preferably a conducting leaf of the element. It may be an extension of a central leaf, located between two piezo-electric bodies, or an extension of the outer layer, in which case it is possible that there is just one piezo-electric body present. In case of elements with a central leaf, both outer layers may be connected to each other and receive energizing voltages, which are higher and lower, respectively, than the voltage on the central leaf.
In this way a cumulative bending action of both piezoelectric bodies is obtained, but the direction of the electric vector in each of said bodies alternates, which may lead to depolarisation. The latter can be prevented by energizing both outer layers separately, in such way that in each of the piezo-electric bodies the voltage is always in the same direction, or there is no voltage at all.
It is possible to apply the method in accordance with the invention to an element which has already been adjusted by means of bending or securing one end, in which case in particular a high reliability can be obtained of, for example, a braille cell that has been fitted with the elements, by means of applying the method in accordance with the invention to an element which has undergone (been subjected to) an aging treatment. Experience has shown that in this way an accurately adjusted element can be obtained as well as an element that in practice no longer can become deranged.
The invention also comprises tools which facilitate the application of the method. A tool, which does not serve to bend a metal strip, but to hold a metal ring, simultaneously supporting it, is known from the patent document U.S. Pat. No. 4,021,922.